The process for the production of a polycarbonate includes a melt polycondensation method (transesterification method) and an interfacial polycondensation method (phosgene method), and the interfacial polycondensation method is industrially preferably employed.
In the process for the production of a polycarbonate based on the interfacial polycondensation method, an emulsion obtained by an interfacial polycondensation reaction is subjected to washing and separation procedures to obtain an organic solvent solution of a polycarbonate (the solvent is generally methylene chloride). Then, the polycarbonate is isolated (recovered) as a powder or particles from the obtained organic solvent solution. Thereafter, the so-obtained polycarbonate is molded in the form of pellets or the like as required.
As a simple method for recovering a polycarbonate as a powder from an organic solvent solution, there is known a method in which the organic solvent solution and steam are introduced into an ejector nozzle (mixing nozzle), the mixture ejected from the ejector nozzle is introduced through a tubing into a separator, and a polycarbonate powder is recovered with the separator (JP-B-63-1333, JP-B-2-6561 and U.S. Pat. No. 3,508,339). For recovering the polycarbonate powder by the above method, the ratio (W.sub.S /W.sub.O) of the weight of the steam (W.sub.S) and the weight of the organic solvent (W.sub.O) in the organic solvent solution of the polycarbonate is set to be greater than 1/5, and the steam and the organic solvent solution are introduced into the mixing nozzle.
The above method has an advantage in that a polycarbonate having a less residual solvent content can be facilely recovered in the form of powder as compared with a method in which a poor solvent is added to an organic solvent solution of a polycarbonate (JP-B-42-14474), a kneader-applied pulverization method taking advantage of the crystallization of an organic solvent solution of a polycarbonate (JP-B-53-15899) or a method in which an organic solvent solution of a polycarbonate is poured into hot water (Japanese Patent Application No. 60-115625).
However, in the conventional method in which an organic solvent solution of a polycarbonate is introduced into a mixing nozzle and the polycarbonate is recovered in the form of a powder from a mixture ejected from the mixing nozzle, the obtained polycarbonate has the form of waste thread, and the bulk density thereof is as low as 0.05 to 0.35. Therefore, the volume efficiency of a treating apparatus used for the post treatment for drying or storage of the obtained polycarbonate powder is low. There is hence a problem in that a treating apparatus having a large size is required or that the production adjustment is required to meet the volume of the treating apparatus. Further, a polycarbonate powder having a low bulk density is poor in the mixability with other additives, and dense pellets cannot be obtained when this powder is pelletized.
It is an object of the present invention to provide a process for the production of a polycarbonate powder having a high bulk density, which can facilely give a polycarbonate powder having a high bulk density and having a less residual solvent content.